Along with a rapid development of various information apparatuses from mobile terminals to large capacity servers, further high performance improvements such as higher integration, increases in speed, and lower power consumption have been pursued in elements such as a memory and a logic configuring this. In particular, a semiconductor non-volatile memory has significantly progressed, and, as a large capacity file memory, a flash memory is spreading at such a rate that hard disk drives are replaced with the flash memory. Meanwhile, the development of FeRAM (Ferroelectric Random Access Memory), MRAM (Magnetic Random Access Memory), PCRAM (Phase-Change Random Access Memory), or the like has progressed as a substitute for the current NOR flash memory, DRAM or the like in general use, in order to use them for code storage or as a working memory. A part of these is already in practical use.
Among them, the MRAM performs the data storage using a magnetization direction of a magnetic material, so that high speed and nearly unlimited (1015 times or more) rewriting can be made, and therefore has already been used in fields such as industrial automation and an airplane. The MRAM is expected to be used for code storage or a working memory in the near future due to the high-speed operation and reliability. However, it has challenges related to lowering power consumption and increasing capacity actually. This is a basic problem caused by the recording principle of the MRAM, that is, the method of inverting the magnetization using a current magnetic field generated from an interconnection.
As a method of solving this problem, a recording method not using the current magnetic field, that is, a magnetization inversion method, is under review. In particular, research on a spin torque magnetization inversion has been actively made (see, for example, Patent Documents 1, 2, and 3, and Non-Patent Documents 1 and 2).
The memory element using a spin torque magnetization inversion often includes an MTJ (Magnetic Tunnel Junction) element and TMR (Tunneling Magnetoresistive) element, similarly to the MRAM.
This configuration uses a phenomenon in which, when spin-polarized electrons passing through a magnetic layer which is fixed in an arbitrary direction enter another free (the direction is not fixed) magnetic layer, a torque (which is also called as a spin transfer torque) is applied to the magnetic layer, and the free magnetic layer is inverted when a current having a predetermined threshold value or more flows. The rewriting of 0/1 is performed by changing the polarity of the current.
An absolute value of a current for the inversion is 1 mA or less in the case of an element with a scale of approximately 0.1 μm. In addition, because this current value decreases in proportion to a volume of the element, scaling is possible. Furthermore, because a word line necessary for the generation of a recording current magnetic field in the MRAM is not necessary, there is an advantage that a cell structure becomes simple.
Hereinafter, the MRAM utilizing a spin torque magnetization inversion will be referred to as ST-MRAM (Spin Torque-Magnetic Random Access Memory). The spin torque magnetization inversion is also referred to as spin injection magnetization inversion. Great expectations are placed on the ST-MRAM as a non-volatile memory capable of realizing lower power-consumption and larger capacity while maintaining the advantages of the MRAM in which high speed and nearly unlimited rewriting may be performed.